title: Reinvestigation of the ambient cistern and its related arachnoid membranes: an anatomical study.
abstract: OBJECTIVE
  A precise understanding of the ambient cistern and its associated arachnoid membranes is helpful for accessing perimesencephalic lesions. However, few studies of the arachnoid membranes related to the ambient cistern have been published, and, additionally, some aspects of the ambient cistern also require further examination. The goal of this study was to reinvestigate and expound on the anatomical features of the cistern and membranes.
  
  
  METHODS
  The ambient cisterns and its associated arachnoid membranes were examined in 20 adult cadaveric brains using an operative microscope.
  
  
  RESULTS
  The perimesencephalic membrane is a set of inner arachnoid membranes surrounding the midbrain at the level of the tentorial incisura. It arises from the outer arachnoidal membranes covering the tentorial edge and the dorsum sellae and can be subdivided into anterior and posterior portions. The anterior membrane is actually the mesencephalic leaf of Liliequist membrane, which is divided into medial and lateral parts by the oculomotor nerve. The posterior membrane can be divided into horizontal and ascending parts. The ambient cistern is located above the perimesencephalic membrane and contains the anterior choroidal arteries, the posterior cerebral arteries, the basal vein, and sometimes the segments of the superior cerebellar arteries. It communicates with the carotid cistern, the interpeduncular cistern, the oculomotor cistern, the cerebellopontine and cerebellomesencephalic cistern, and the quadrigeminal cistern.
  
  
  CONCLUSIONS
  This study updates some information about the ambient cistern and its arachnoid membranes. The perimesencephalic membrane was identified and described in detail. The ambient cistern was verified to be a supratentorial cistern above the perimesencephalic membrane. The borders and contents of this cistern, as well as its relationship with adjacent cisterns, were also redefined.
authors.affiliation: Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China. nfsjwk@gmail.com
authors.forename: Song-tao
authors.initials: ST
authors.lastname: Qi
authors.forename: Jun
authors.initials: J
authors.lastname: Fan
authors.forename: Xi-an
authors.initials: XA
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Pan
mesh_terms: D000328:Adult; D001099:Arachnoid / Q000033:anatomy & histology*; D002102:Cadaver; D002946:Cisterna Magna / Q000033:anatomy & histology; D006801:Humans; D008566:Membranes / Q000033:anatomy & histology; D008636:Mesencephalon / Q000033:anatomy & histology*; D008866:Microsurgery / Q000379:methods; D013346:Subarachnoid Space / Q000033:anatomy & histology